LITTLE ROCK, Ark. (KTHV) — Little Rock police arrested 21-year-old William Alexander Monday afternoon for the murder of 24-year-old Mariah Cunningham and her two children. He's facing three counts of capital murder and is being held without bond.

“We've been waiting for this breakthrough,” said Derykka Miller, Cunningham's cousin who FaceTimed us out of Atlanta.

Cunningham and her children, 5-year-old A'Layliah and 3-year-old Elijah were found dead inside their Little Rock apartment home on Dec. 4. A family member found them after deciding to check on them because the children never showed up to school.

Miller doesn't know details about the relationship between Cunningham and Alexander, but knows they were acquaintances.

“I can't tell you how close they were, but I know that they knew each other,” Miller said.

It's been over a month since the murders happened, leaving the family eager with questions. They're thankful to see steps taken by detectives in the case.

“They ensured us they were diligently working the case so we are glad to see the pieces of the puzzle coming together,” Miller said.

Cunningham was a single mom working two jobs. Miller describes here as a kind soul.

“She would just open up her house to anyone and that's the problem, I think, here. She was so spirited and would try to help anyone that I think they took that kindness for a weakness,” Miller said.

Miller believes there are more people involved and police expect more arrests to come.

“Justice has prevailed now that we have someone in custody and to know they are still anticipating additional arrests, we are happy. It gives us a little bit of closure,” Miller said.

Police have not released a motive behind the murders.